DE1085164B - Process for the production of aniline by catalytic reduction of nitrobenzene - Google Patents

Description

Process for the production of aniline by catalytic reduction of nitrobenzene The present invention relates to a process for the preparation of aniline from nitrobenzene by catalytic reduction using a new one Catalyst obtained by impregnating silicon oxide hydrogel with a solution of a Cuprammonium compound, drying and calcining in a reducing atmosphere has been made.

The catalytic properties of copper and its salts, for example in the reduction of aromatic nitro compounds, the dehydration of alcohols, the oxidation of hydrocarbons and alcohols or the hydrogenation of double bonds have been known in the art for many years. Lots of catalysts are has been described as useful for these purposes. For example, it has been suggested To use molten copper oxide, a gel of copper (II) chloride and sodium silicate to manufacture metallic copper on alumina or a copper salt on one Knock down carriers such as pumice stone, asbestos or diatomaceous earth.

The catalysts described so far in the literature have serious Disadvantages on. The conversion of nitrobenzene to aniline, for example, does not take place quantitatively. Another disadvantage of the catalysts known hitherto is their difficulty Depiction.

A more significant disadvantage of the catalysts known to date is their short lifespan. Certain catalysts, especially those that Copper as a basis are easily poisoned or by tarry or carbonaceous Precipitation contaminates, causing a decrease in their activity will. If this occurs, the catalytic process must be interrupted in order to remove the Regenerate catalyst. Experiments have shown that the previously known Catalysts not regenerated in an economical manner and therefore not repeatedly can be used with advantage for large-scale systems.

Another disadvantage of the catalysts known to date is that many of them cannot be obtained in flowable form. The development the art of flowable catalysts in recent years; d. H. the catalytic converters, which are finely divided and can be pumped through the manufacturing facility as if they were liquids, it has the economics of catalytic processes much improved. These catalysts can be used for continuous processes can be used and removed from the reaction mixture by settling, filtering or the like Measures are separated and fed back to the feed. The catalysts can be removed from the reaction hinge, 1 separate and then into the reaction chamber to be led back. Many of the catalysts known to date cannot be used in one particle size suitable for flowable catalysts can be prepared. Others Catalysts lack the structural strength required for free-flowing catalysts is required.

For this purpose, the production of one for the reduction of aromatic nitro compounds usable copper catalyst suggested by Deposition of copper on a support described in which a silica hydrogel is made by precipitating silica at a p-value between 3 and 10 and this hydrogel with the solution of a copper-ammonium complex cation at a pE value between 8 and 12 is impregnated, the impregnation mixture at least Contains 0.085 parts by weight of copper per part by weight of silicon oxide. The impregnated Hydrogel is evaporated, washed, dried and then at one temperature between 150 and 3500 C in a hydrogen atmosphere. You get one like that copper catalyst suitable for the reduction of aromatic nitro compounds, that of a homogeneous dispersion of copper distributed in a silicon oxide carrier and the flow properties resembling a liquid, a copper content of at least 5 percent by weight, an effective surface area of at least 200 m2 / g, a pore volume of over 0.25 ccm / g and pore diameter of at least Has 20 angstrom units.

It has now been found that aniline can be extracted in an excellent manner Nitrobenzene and hydrogen can be produced using a mixture of nitrobenzene vapor and excess hydrogen in a reaction zone with such a copper catalyst contacted. The reaction temperature is 150 to 3500 C, preferably 250 to 3000 C.

To better explain the production of aniline from nitrobenzene in the presence of the above-mentioned catalyst, reference is made to the drawing.

In this, 1 means a nitrobenzene evaporator, 2 a reactor, containing a flowable catalyst bed, 3 a heat exchange device for Removal of the exothermic heat of reaction, 4 filters that entrain the flowable Prevent a catalytic converter, 5 a condenser, 6 a compressor for the hydrogen return, 7 a sedimentation vessel for the separation of aniline and water due to the gravity, 8 a dehydration column for the aniline, 9 a reboiler for the dehydration column, 10 a condenser for the dehydration column, 11 a roller blind for cleaning of the aniline, 12 a reboiler for column 11, 13 a condenser for column 11 and 14, a heating element for the evaporator 1.

In the method according to the invention, the reactor 2 is initially with charged to the above-mentioned catalyst. For the production of an active catalyst it is advantageous to carry out the reduction in the reactor. Before adding hydrogen the system is cleaned of air. This is done with an inert gas such as nitrogen or carbon dioxide, to avoid a flammable mixture. The reduction is generally carried out at 2500 C. The heat required is through Preheating of the hydrogen and fed through the heat exchanger 3.

After reducing the catalyst, nitrobenzene is turned on by an automatic Device placed in the vaporizer 1, the automatic device being a uniform filling speed guaranteed. The evaporator 1 is through the Heizelementl4 heated. A mixture of nitrobenzene from the evaporator and excess Hydrogen gas enters reactor 2. The reaction gases flowing into the reactor 2 consist preferably .aus approximately 10 to 20 mole percent nitrobenzene and 80 to 90 mole percent hydrogen.

The mixture of nitrobenzene vapor and hydrogen flows upwards through a porous distributor plate into the reaction chamber. The catalyst powder is carried up through the chamber with the flow of gas. The grille at the bottom the reaction chamber is perforated with holes of such size and number that a pressure drop of approximately 0.07 ata is created. This is used to distribute the Gases all over the catalyst bed and to generate gas flows for mixing of gas and catalyst in bed. The holes in the grid must be big enough to prevent clogging by catalyst particles. Under reaction conditions, the gases have for example 1.4 ata and 2700 C a density of about 600 / o the density of Air under standard conditions. The steam speed in reactor 2 is approximately 30cm / second.

The reduction of nitrobenzene is strongly recommended.

Heat exchange fluid circulates through the outlet exchanger 3 to remove excess heat of reaction. The diameter of the catalyst bed is determined by the throughput speed. The height of the catalyst bed should be sufficient to ensure a full response and a sufficient one To achieve catalyst volume, so that a regeneration of the catalyst only in large intervals is required. This requires a data: lysatorbett whose Height is greater than its diameter. The upper part of the reactor 2, which is practically is empty, acts as a separation zone, which allows a larger part of the gas flow entrained catalyst particles fall back into the bed. The escaping gases are removed from the catalyst by filtration through the porous stainless steel filters4 freed. The filtered gases are cooled in the condenser 5, the aniline and water from the excess hydrogen, which is returned to the reactor, separates.

The aniline is separated from the water by allowing it to settle in chamber 7. The moist aniline passes through column 8. The dry aniline from the bottom of the column 8 is fractionated in column 11 and gives a pure product of high quality Water and aniline vapors leaving column 8 at the top are condensed and returned to the sedimentation vessel 7.

The process described above produces aniline in over 990% Yield of theory. After a certain time, the catalyst activity decreases. which is caused by the deposition of organic material on the catalyst with considerable amounts of nitrobenzene being contained in the condensed aniline. When nitrobenzene begins to appear in significant quantities in the condensed aniline. regeneration of the catalyst is required. This can be done easily by stopping the nitrobenzene supply and purging the system with inert gas and flowing through of the catalyst can be achieved with air at about 250 to 3500 C. The organic Precipitation is burned here. Probably at least one will Part of the metallic copper is converted into an oxide. To prevent excess heat To avoid regeneration, an air / water vapor mixture is used at the beginning.

The regeneration with air is terminated if only a small amount of precipitation remained and therefore the rate of heat release is only slight.

After the catalyst has been regenerated, any copper oxide formed is formed by flowing an inert gas through the system and reducing with hydrogen reduced at about 2500 C. This represents a repetition of the method step described above The nitrobenzene supply is resumed and the cycle is repeated, as long as the catalyst has an essentially quantitative reduction of nitrobenzene to aniline is able to perform.

It is known that copper catalysts are easily replaced by sulfur compounds to be poisoned. In order to achieve the longest possible service life for the catalytic converters, Therefore, preference is given to using nitrobenzene, which has less than 10 parts NifrothiopheivMillion Contains parts. P-enzene synthesized from petroleum fractions is generally relatively thiophene-free. Benzene from coal tar can be thiophene-free by known processes be made. The life of a catalytic converter is inversely proportional to Amount of nitrothiophene present in the nitrobenzene. A maximum of 10 parts thiophene / million Parts Nitrobenzene ensures a total service life of more as 600 g aniline catalyst.

The method according to the invention imposes certain limitations on the throughput rate the reaction mixture. If the gas flow is too slow, the catalyst will not work made flowable. If the gas flow is too fast, the reactants will run out of the reaction chamber removed before sufficient contact to perform a quantitative reduction was possible. The linear velocity of the gas flow should be 3 cm to 1.5 milliseconds with sufficient catalyst present, a contact time between 0.5 and achieve 100 seconds.

Example Nitrobenzene was reduced to aniline in a device, those from an electrically heated evaporator, a glass reactor with a diameter of 2.5 cm and a length of 51 cm, a glass tube with a diameter of 15 cm for settling and returning entrained catalyst parts and a condensation system duration. The reactor was initially loaded with 50 parts of one according to the above obtained, unreduced catalyst powder which contained 9.5 9.5% copper, charged, heated to 2600 C and hydrogen until the complete reduction of the Catalyst passed through.

Then nitrobenzene and hydrogen were added to 220-2300 C heated evaporator and passed as a mixture in an amount of 54 parts of nitrobenzene and 7.9 parts hydrogen / hour continuously through a porous distributor plate Introduced below into the heated to 2600 C, vertically arranged reactor. The catalyst particles were carried up the reactor by the gas stream. The catalyst particles entrained from the reactor were in the above-mentioned Sedimentation vessel collected and returned to the reactor.

The experiment was allowed to run until the reaction product was 0.5% nitrobenzene contained. Until this one Point in time was 119 parts of nitrobenzene per part of catalyst been reduced to aniline.

After stopping the nitrobenzene supply, clean the system first with hydrogen, then with nitrogen, passing air through until all carbon dioxide is present was driven off and nitrogen bubbling again became the catalyst completely reduced again with hydrogen.

The cycle (nitrobenzene reduction and reduction of the catalyst) was repeated until the catalyst had to be discarded. All in all 443 parts of nitrobenzene per part of catalyst were reduced to aniline.

PTENTAN APPROACH: 1. Process for the production of aniline by catalytic Reduction of nitrobenzene, characterized in that there is a mixture of nitrobenzene vapor and excess hydrogen in a reaction zone with a copper catalyst contacted, which consists of a homogeneous dispersion of in a silica carrier distributed copper, which has liquid-like flow properties and is in this state during the reaction, has a copper content of at least 5 percent by weight, an effective surface area of at least 200 m2 / g, a pore volume of over 0.25 ccm / g and a pore diameter of at least 20 angstrom units and that the aniline formed from the accompanying water is then passed through Evaporation separates.

Claims (1)

2. The method according to claim 1, characterized in that the reaction zone is maintained at 150 to 3500 by means of a heat exchanger. 3. The method according to claim 1 and 2, characterized in that one at a linear velocity of the gas flow of 3 cm to 1.5 m / second and a catalyst contact time of 0.5 to 100 seconds works.